MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 257 PM EDT THU MAR 31 2016 VALID MAR 31/1200 UTC THRU APR 04/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 12Z NAM/GFS ALONG WITH PRELIMINARY PREFERENCES/FORECAST CONFIDENCE... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...LEAD SHORTWAVE CURRENTLY MOVING THROUGH THE MIDDLE MS VALLEY... ...SURFACE WAVE STRENGTHENING OVER WESTERN QUEBEC... ...EXPANSIVE COLD FRONT CROSSING THE I-95 CORRIDOR BY 02/0000Z... PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/ECMWF/UKMET FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE AMIDST A SERIES OF SHORTWAVES TRAVERSING THE CENTER OF THE COUNTRY...THE LEAD IMPULSE CURRENTLY FOCUSING CONVECTION ACROSS CENTRAL/EASTERN IL SHOULD QUICKLY LIFT NORTHEASTWARD REACHING THE LOWER GREAT LAKES BY THIS EVENING. MODELS CLUSTER WELL AS THE SYSTEM ACCELERATES TOWARD QUEBEC WITH INTENSITY AND POSITION GENERALLY AGREED UPON. REGARDING THE COLD FRONT WHICH WILL STRETCH FROM NEW ENGLAND DOWN TO THE CENTRAL GULF OF MX ON FRIDAY EVENING...THE 12Z NAM/09Z SREF MEAN ARE MORE AGGRESSIVE WITH SURFACE LOW FORMATION ALONG THE LA COAST WHILE ALSO BEING MUCH SLOWER IN NATURE. TO A LESSER EXTENT...THE 12Z/00Z CMC SHOWS MODEST SUPPORT FOR THIS SOLUTION BUT THESE FORECASTS ARE IN THE MINORITY. WILL LEAN TOWARD THE STRONGER CONSENSUS FORMED BY THE 12Z GFS/ECMWF/UKMET. ...SECONDARY SURGE/WAVE PUSHING THROUGH THE UPPER GREAT LAKES BY EARLY SATURDAY MORNING... ...ENHANCED LOBE OF VORTICITY LEAVING THE NJ COAST BY THE FOLLOWING MORNING... PRELIMINARY PREFERENCE: BLEND OF THE 12Z ECMWF/00Z ECMWF ENSEMBLE MEAN FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE MODELS ARE UNANIMOUS IN CARRYING A MORE SIGNIFICANT BAND OF HEIGHT FALLS THROUGH THE GREAT LAKES REGION EARLY IN THE WEEKEND. THE PAST COUPLE OF ENSEMBLE SPAGHETTI PLOTS SHOW MANY OF THE ECMWF ENSEMBLE MEMBERS ARE SLIGHTLY MORE AMPLIFIED RELATIVE TO THE CONSENSUS. GIVEN THE DEPTH OF THE UPPER TROUGH...THIS DOES NOT LOOK TERRIBLY UNREASONABLE. MEANWHILE...THE GFS SOLUTIONS ARE MUCH QUICKER WHICH COULD PERHAPS BE RELATED TO ITS OFTEN QUICK BIAS. THE LARGEST UNCERTAINTY IN THE FORECAST IS REGARDING THE STRENGTH OF THE CYCLOGENESIS TAKING SHAPE IN THE VICINITY OF THE NEW ENGLAND COAST. THE 12Z NAM/UKMET ARE RATHER DEEP CARRYING NEAR 980-MB SOLUTIONS ON SUNDAY MORNING. WILL CONTINUE TO PLAY IT A LITTLE MORE CONSERVATIVELY FAVORING THE 12Z ECMWF WHILE INCLUDING ITS MEAN GIVEN THE INCREASING UNCERTAINTY. THIS IS STILL A DAY 3 FORECAST SO A LOT WILL LIKELY CHANGE OVER THE COURSE OF THE NEXT FEW MODEL CYCLES. ...INITIAL SHORTWAVE MIGRATING ACROSS NORTHERN MX TONIGHT... ...GENERAL WEST-EAST BAND OF VORTICITY ANCHORING 30N LATITUDE... PRELIMINARY PREFERENCE: BLEND OF THE 12Z ECMWF/UKMET FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE WATER VAPOR IMAGERY AND OBJECTIVE ANALYSES SHOWED A POSITIVELY-TILTED UPPER TROUGH ACROSS SOUTHERN AZ/FAR NORTHWESTERN MX. THIS SYSTEM IS FORECAST TO ADVANCE EASTWARD REACHING THE SOUTHERN PLAINS BY FRIDAY EVENING. THE MORE ROBUST NATURE OF THE 12Z NAM SEEMS TO FAVOR THE DEEPER SURFACE SOLUTION ACROSS THE LOWER MS VALLEY WHICH RULES THIS FORECAST OUT VIA THE FIRST SECTION. EVENTUALLY THE EVOLUTION OF THIS SYSTEM BECOMES MORE COMPLICATED AS SOME OF THE SHORTWAVE ENERGY JOINS THE ACTIVE NORTHERN STREAM WHILE REMNANT VORTICITY LINGERS OVER THE SOUTHERN TIER. ADDITIONALLY...AN UPSTREAM TROUGH FROM WESTERN MX ADJOINS THE THE TRAILING BAND OF ENERGY STRETCHING ALONG THE GULF COAST REGION DURING THE WEEKEND. THE 12Z GFS/GEFS MEAN REMAIN MORE PROGRESSIVE WHILE THE 12Z ECMWF/UKMET ARE SLIGHTLY MORE CONSERVATIVE. GIVEN THE COMPLEX EVOLUTION OF THESE MANY WAVES...WILL STICK WITH THE SLOWER FORECAST FAVORING A BLEND OF THE 12Z ECMWF/UKMET. ...WEAK PACIFIC IMPULSE CROSSING THE NORTHWESTERN U.S. ON SATURDAY MORNING... PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/ECMWF FORECAST CONFIDENCE: AVERAGE AN EXPANSIVE UPPER RIDGE CURRENTLY EXTENDING ALONG THE EASTERN PACIFIC/WEST COAST FROM 40N LATITUDE UP TO BRITISH COLUMBIA WILL BREAK DOWN AS MODEST HEIGHT FALLS APPROACH THE PACIFIC NORTHWEST COAST. BY SATURDAY MORNING...THE BEST POSITIVE VORTICITY ADVECTION SHOULD BE CROSSING THE REGION WITH SOME DIFFERENCES IN TIMING AMONG THE GUIDANCE. THIS SYSTEM WILL CONTINUE TO SHEAR WHICH LEADS TO ONLY MINIMAL SENSIBLE WEATHER EFFECTS. WITH REGARDS TO UNCERTAINTY...THE 12Z NAM/GFS ARE AHEAD OF THE SLOWER 12Z ECMWF WHILE THE 12Z CMC/UKMET ARE SOMEWHERE IN THE MIDDLE. WPC WILL SPLIT BETWEEN THE TWO EXTREMES FAVORING A MIX OF THE 12Z GFS/ECMWF. ...MORE PRONOUNCED HEIGHT FALLS APPROACHING THE WEST COAST BY THE END OF THE WEEKEND... PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/ECMWF FORECAST CONFIDENCE: ABOVE AVERAGE TOWARD THE END OF THE PERIOD...MORE SUBSTANTIAL UPPER TROUGHING TAKES SHAPE ACROSS THE EASTERN PACIFIC WHICH IS SUPPORTED BY A STRONG SIGNAL IN ALL OF THE GUIDANCE. THE MULTI-DAY TRENDS PER SPAGHETTI PLOTS HAS SHOWN A MOVE IN THE FASTER DIRECTION. A FAIRLY STRONG CONSENSUS IS FORMED BY THE GFS/ECMWF SOLUTIONS WITH ONLY A SMALL HANDFUL OF MEMBERS BEING SLOWER/MORE AMPLIFIED. THE 12Z/00Z CMC ALONG WITH THE 12Z NAM LAG WELL TO THE WEST. THIS NOTABLE SLOWING IN THE CMC HAS BEEN EVIDENT IN ITS PAST FEW MODEL CYCLES AS WELL. THE BEST COURSE OF ACTION HERE IS TO FOLLOW THE CLUSTER FORMED BY THE 12Z GFS/ECMWF. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER